ANIMAL EVOLUTION 



539 



Ordovician and pre-Ordovician animals 

 becomes more evident if we contemplate 

 the missing types, which are the follow- 

 ing: the ctenophores, flatworms and 

 roundworms, rotifers and gastrotrichas, 

 priapulids and sipunculids, heteropods, 

 archiannelid, oligochxte, myzostomid, 

 hirudinid and onychophorid worms, 

 nemerteans, phoronids, insects, ptero- 

 branchiates, balanoglossids, tunicates, and 

 vertebrates other than fishes. 



Except for the insects and the verte- 

 brates, which are primarily terrestrial, 

 all of these various types are soft bodied 

 creatures which cannot reasonably be 

 expected to occur as fossils, since they can 

 only be preserved as such by the merest 

 accident. 



This long list of animal types repre- 

 sented by the fossils in the Cambrian and 

 immediately succeeding rocks can have 

 only one meaning. It shows conclusively 

 that as far back as Cambrian time the 

 status of the animal world was, in its 

 broader features, just what it is today. 



So we see that the fossil record, the 

 actual history of the animal life upon the 

 earth, bears us out in the assumption that 

 at its very first appearance animal life in 

 its broader features was in essentially the 

 same form as that in which we know it 



)W. 



Of course it is quite likely, indeed it is 

 most probable, that animals existed long 

 before the commencement of the fossil 

 record. But in this case, judging from the 

 correspondence between the animals of 

 the Cambrian and those of the present 

 day, we may safely predicate a similar 

 correspondence between the animals of 

 the Cambrian and those of a more distant 

 past. 



EVOLUTION WITHIN THE MAJOR GROUPS 



Thus so far as concerns the major groups 

 of animals, the creationists seem to have 



the better of the argument. There is not 

 the slightest evidence that any one of the 

 major groups arose from any other. Each 

 is a special animal complex related, more 

 or less closely, to all the rest, and appear- 

 ing, therefore, as a special and distinct 

 creation. 



But within each major group we see a 

 very different picture. Here the fossil 

 record shows a constant change from one 

 horizon to another. These successive 

 variations are probably simply indications 

 of a direct response to physical alterations 

 in environment favoring now one type 

 or subtype, now another. 



This continuous alteration in the ele- 

 ments within the various groups is what 

 is commonly known as evolution. It is 

 perhaps best illustrated in the vertebrates, 

 since these are the most familiar of the 

 animals. 



The evolution of the reptiles from the 

 Carboniferous to the end of the Cretaceous, 

 and of the mammals from the end of the 

 basal Eocene to the present day, or rather 

 to the period just past (Pleistocene), 

 forms a story of most absorbing interest. 

 Here we can trace the gradual develop- 

 ment from comparatively insignificant 

 beginnings to a wonderful flowering of 

 specialization and perfection. 



So much has been written on this 

 subject, especially in recent years, that it 

 seems unnecessary here to pursue it further. 



But it is well to emphasize that every 

 evolutionary line has certain gaps; some 

 have these gaps large and broad, while in 

 others (as in the horses) the gaps are 

 relatively small. These gaps probably 

 are largely natural, and not due to a 

 deficiency in the record. They indicate 

 the continuation of the phylogenetic 

 line through variants showing a more or 

 less wide departure from the normal type 

 which happened best to meet the con- 

 ditions of the time. We observe plenty 



